Electric switch having oppositely operating dual contacts

ABSTRACT

In an electric switch for use in inductive circuits including main contacts connected in series with the circuit and short circuit contacts connected in parallel with the circuit, both of the main and short circuiting contacts are driven by a common source of motive power through discrete operating mechanisms. The operating mechanism for the short circuiting contacts includes a lever of variable length which is connected to a contact carrying arm through a lost motion coupler.

United States Patent Inventors Appl. No. Filed Patented Assignee Priority Hiroshi Koike;

Rokuro Fujita, both of Tokyo-to, Japan 854,142

Aug. 29, 1969 Oct. 19, 1971 Tokyo Shibaura Denki Kabushiki Kaish also known as Tokyo Shibaura Electric Co., Ltd.

Kanagawa-ken, Japan Sept. 4, 1968 Japan ELECTRIC SWITCH HAVING OPPOSITELY OPERATING DUAL CONTACTS 4 Claims, 7 Drawing Figs.

U.S. Cl 200/146 R Int. Cl ..H01h 33/12 Field of Search 200/ 146, 144

[56] References Cited UNITED STATES PATENTS 724,228 3/1903 Wood 200/l44 790,983 5/l905 Rucker 200/146 3,501,606 3/1970 Harper 200/146 Primary Eiaminer-Robert S. Macon Att0rneysRobert E. Burns and Emmanuel J. Lobato ABSTRACT: In an electric switch for use in inductive circuits including main contacts connected in series with the circuit and short circuit contacts connected in parallel with the circuit, both of the main and short circuiting contacts are driven by a common source of motive power through discrete operating mechanisms. The operating mechanism for the short circuiting contacts includes a lever of variable length which is connected to a contact carrying arm through a lost motion coupler.

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BACKGROUND OF THE INVENTION This invention relates to an electric switch for interrupting inductive loads such as field circuits of dynamoelectric machines and coils of induction furnaces.

Switches utilized in such applications are generally provided with .main contacts and auxiliary or short circuiting contacts which are closed prior to the opening of the main contacts to short circuit the inductive load, preferably through a current limiting or discharge resistance, to dissipate the electromagnetic energy stored in the inductive load, thus relieving the main contacts from interrupting excessively large current.

Switches of this type are required to be constructed to satisfy the following relations:

I. The order of operation of the main and short circuiting contacts should be opposite. More particularly, when the main contacts are opened, the short circuiting contacts are closed, and vice versa.

Z/During the opening and closing operations, both the main and short circuiting contacts should be in their closed state for a predetermined short interval.

In prior switches it was necessary to employ complicated mechanisms to adjust the time relationship between opening and closing of the main and short circuiting contacts. Such mechanisms are expensive and are difficult to maintain, inspect and repair.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a novel electric switch for use in inductive circuits wherein the time relationship between closing and opening of the main contacts and-short circuiting contacts can be readily adjusted.

' Another object of this invention is to provide an electric switch, more particularly a field switch, which is easy to fabricate, inspect, adjust and repair.

In accordance with the invention, an electric switch assembly is provided including two sets of switch contacts having separate actuating arms for operation by a single moving member, said switch including mechanism for opening and closing the two sets of contacts in opposition, and for causing each set of contacts to make, as they are being closed, before break" of the contacts which are being opened. F urthermore, adjustable means are included in such mechanism for controlling the time duration in which both sets of contacts are simultaneously closed during the switching operation. Thus, the switch assembly is highly useful for inductive circuits,.wherein an inductive load current is carried by a main set of said contacts, said main contacts being protected against harmful arcing due to inductive pulses by means of the other set of contacts which are connected to short circuit the inductive load just prior to opening of the main set of contacts.

More particularly, according-to a preferred embodiment of this invention there is provided an electric switch for use in an inductive circuit comprising a pair of cooperating main contacts adapted to be connected in series with said circuit, a pair of cooperating short circuiting contacts adapted to short circuit said inductive circuit, a source of motive power, a first operating mechanism driven by said source of motive power to open and close said main contacts, and a second operating mechanism driven by said source of motive power to open and close said short circuiting contacts, said second operating mechanism including a pivoted arm carrying one of said short circuiting contacts, a spring to normally bias said pivoted arm to close said short circuiting contacts, a lever interconnecting said source of motive power and said pivoted arm, means to adjust the effective length of said lever and a lost motion coupling means between said lever and said pivoted arm. The lost motion coupling means is constructed and arranged in a manner such that the short circuiting contacts are maintained in their closed state when said main contacts are being opened, whereas the short circuiting contacts are maintained in their opened state when the main contacts are being closed. The time relationship of closing and opening of the main and short circuiting contacts are varied by varying the effective length of the lever and the position of the stationary short circuiting contact.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. 1 is a side view of the short circuiting contacts shown in closed state and their operating mechanism of a field switch constructed according to the principle of this invention;

FIG. 2 is view similar to FIG. 1 but showing the short circuiting contacts in their opened state;

FIG. 3 is a side view of the main contacts shown in opened state and their operating mechanism of the field switch;

FIG. 4 is a schematic illustration of the switch contacts of FIGS. 1 and 3 showing the relative positions of the main and short circuiting contacts when the main contacts are fully open;

FIG. 5 is a view similar to FIG. 4, in which the respective contacts are shown in a position of simultaneous actuation wherein the main contacts are partially closed, and wherein the short circuiting contacts remain closed;

FIG. 6 is a view similar to FIGS. 4 and 5, but shows the respective contacts when the main contacts are partially closed further than in FIG. 5, and wherein the short circuiting contacts are open; and

FIG. 7 is a view similar to FIGS. 4-6, in which the main contacts are shown as being fully closed, and the short circuiting contacts are shown as being fully open. I

DESCRIPTION OF THE PREFERRED EMBODIMENT In the following the invention is shown and described as applied to a field switch for dynamoelectric machines, but it should be understood that this is a mere illustration of the use of the novel switch and that the switch is useful for interrupting any type of inductive loads.

As shown in the accompanying drawing, a crossbar 8 operated by a source of motive power, such as an electromagnet, an electric motor, or a fluid pressure cylinder, not shown, is connected to a lever 10 through an adjustable coupling 9, the opposite end of the lever being provided with a longitudinal elongated slot II to receive a supporting stub shaft 13 of a roller 12. Stub shaft 13 is also received in a groove I6 of a stationary arm of frame I5 mounted on a supporting panel 14. As a result, when crossbar 8 is reciprocated as shown by arrows by the source of motive power the stub shaft I3 is caused to slide along inner walls of slot I1 and groove 16 thus reciprocating roller I2 along groove 16.

A movable arm 18 carrying one of the short circuiting contacts, 20a, is pivotally mounted on a pivot pin I7 secured to arm 15. A roller 19 is mounted on the opposite end of movable arm 18. A tension spring 21 is interposed between panel 14 and movable arm 18 to normally bias the later in the clockwise direction to cause contact 20a to engage the other short circuiting contact 20b secured to panel 14 through an adjustable spacer 22.

FIG. 3 shows an operating mechanism for the main contacts, comprising a first pair of arcing contacts 270 and 27b, an intermediate pair of arcing contacts 280 and 28b and a pair of main contacts 290 and 29b. A movable arm 26 carrying movable contacts 27a, 28a and 29a is pivotally mounted on a pivotal pin 25 and is connected to crossbar 8 through a lever 24. Thus, as the crossbar is moved toward the right as viewed in FIG. 3, the movable arm 26 is rotated in the clockwise direction to successively close contact pairs 27a, 27b; 28a, 28b and 29a, 29b in the order mentioned. Conversely, when the crossbar is moved in the opposite direction, the movable arm 26 is rotated in the counterclockwise direction to open said contact pairs in the order opposite to that of closing.

The operating mechanism for the short circuiting contacts as shown in FIGS. 1 and 2 and that for the main contacts as shown in FIG. 3 are related to each other in the following manner. It is to be understood that these operating mechanisms are mounted on the same panel .14 in side-by-side relationship and are operated by the same crossbar or source of motive power at the same time. As mentioned hereinabove, the main and short circuiting contacts must fulfil the aforementioned requirements. More particularly, when the main contacts are opened, the short circuiting contacts must be maintained in their closed state as shown in FIGS. 3 and 4. With reference to FIGS. 3 and 4, as the crossbar 8 is driven toward the right, rollers 12 and 12 engage each other to move roller 12 to the left-hand end of slot 11. Meanwhile, movable arm 26 .of the main contacts is rotated in the clockwise direction to close the first pair of arcing contacts 270 and 27b as shown in FIG. 5.

As the movement of the crossbar is continued, the movement of lever 10 is directly transmitted to roller 19 through roller 12, which is now held stationary at the left-hand end of slot 11 to rotate the movable arm 18 in the counterclockwise direction to open short circuiting contacts 200 and b as shown in FIG. 6. Meanwhile, the intermediate pair of arcing contacts 28a and 28b and the main contact pairs 29a and 2% are closed successively as shown in FIG. 7.

Thus, in the closing operation of the main contacts, after the first pairs of arcing contacts 27a and 27b have been closed, the intermediate arcing contacts 28a and 28b and the main contacts 29a and 2% are closed substantially concurrently with the opening of the short circuiting contacts 20a and 20b.

The relationship between times of opening and closing of the main and short circuiting contacts can be simply adjusted by adjusting the length of coupling 9 and/or the thickness of spacer 22.

.When crossbar 8.is moved toward the left as viewed in FIG. 2, roller 12 is freed from the left-hand end of slot 11, and the am 18 is rotated in the clockwise direction under the bias of spring 21 to close short-circuit contacts 20a and 20b with the result that roller 19 urges roller 12 against the left-hand end of groove 16. Meanwhile, main contacts 29a, 29b and intermediate arcing contacts 28a, 28b are opened, respectively, as shown in FIG. 4. Upon further movement of crossbar 8 toward the left the first pair of arcing contacts 27a and 27b are separated as shown in FIG. 3.

Thus, in the opening operation of the main contacts, substantially concurrently with the opening of main contacts 29a, 29b and the intermediate pair of arcing contacts 28a, 28b the short circuiting contacts 20a and 20b are closed as shown in FIG. 6, and thereafter the first pair of arcing contacts 27a and 27b are opened.

In summary, FIGS. 4-7 show the relative positions of the two sets of contacts at various positions of advancement, or withdrawal, of the element 8. For example, as described above, FIG. 4 illustrates the condition where the crossbar 8 is completely withdrawn, so that the short circuiting contacts 20a, 20b are closed under the force of the spring 21 shown in FIGS. 1 and 2. Accordingly, since the contacts operate oppositely, the main contacts 27-29 are all shown in an open condition in FIG. 4. Then, H6. 5 shows the relative positions of the contacts under partial advancement of element 8, wherein both contacts are closed at the same time; that is, contacts 20a, 20b of the short circuiting switch are closed, and contacts 27a, 27b are closed, while contacts 28a, 28b and 29a, 29b, remain open. FIG. 6 shows another intermediate position of the element 8 wherein the main contacts are closed and the short circuiting contacts are open, and FIG. 7 shows the relative positions of the contacts when the element 8 is fully advanced so that all three pairs (27, 28 and 29) of main contacts are closed to conduct the load current.

As can be noted from,the foregoing description, this invention provides an improved electric switch comprising main contacts and auxiliary or short circuiting contacts wherein the time relationship between opening and closing of the main and short circuiting contacts can be simply varied by adjusting the thickness of spacer 22 and adjustable coupling 9. Moreover, as the mam and short circuiting contacts are actuated by separate operating mechanisms activated by a single source of motive power, fabrication, inspection and repair of the switch are easy.

While the invention has been shown and described in terms of a single preferred embodiment, many changes and modifications will be obvious to those skilled in the art within the true spirit of this invention. Thus, for example, the intermediate pair of arcing contacts may be omitted. Further, if desired, an additional adjustable coupling may be provided between crossbar 8 and lever 24 of the main contacts.

We claim:

1. An electric switch assembly having opposingly operating dual sets of contacts for use in preventing high inductive pul ses encountered in the switching of an inductive circuit, comprising a pair of cooperating main contacts adapted to be connected in series with said circuit, a pair of cooperating short circuiting contacts adapted to short circuit said inductive circuit, first operating mechanism means connected to said main contacts for movement to open and close said main contacts, and second operating mechanism means connected to said short circuiting contacts for movement to open and close said short circuiting contacts, means interconnecting said firstand second mechanism means for providing simultaneous movement thereof, said second operating mechanism means including a stationary member, an arm pivotally mounted on said stationary'member and carrying one of said short circuiting contacts, a spring to normally bias said pivotal arm to close said short circuiting contacts, a lever interconnected at one end to said interconnecting means, means to adjust the effective length of said lever, and a lost motion coupling means between the other end of said lever and said pivotal arm.

2. An electric switch assembly according to claim 1 further comprising means for adjusting the position of the stationary contact of said pair of short circuiting contacts in the direction of said movable contact.

3. An electric switch assembly according to claim 1 wherein said means for adjusting the effective length of said lever comprises an adjustable coupling interposed between said interconnecting means and said one end of said lever.

4. An electric switch assembly according to claim 1 wherein said lost motion coupling means comprises means defining an elongated slot in said other end of said lever, a first roller having a shaft slidably received in said slot, said stationary member including elongated groove means to slidably receive said shaft of said roller, a second roller mounted on said pivotal arm to cooperate with said first roller to thereby maintain said short circuiting contacts in their closed state, upon closing of said main contacts, until after said main contacts are closed, and to maintain said main contacts in their closed state, upon closing of said short circuiting contacts, until after said short circuiting contacts are closed. 

1. An electric switch assembly having opposingly operating dual sets of contacts for use in preventing high inductive pulses encountered in the switching of an inductive circuit, comprising a pair of cooperating main contacts adapted to be connected in series with said circuit, a pair of cooperating short circuiting contacts adapted to short circuit said inductive circuit, first operating mechanism means connected to said main contacts for movement to open and close said main contacts, and second operating mechanism means connected to said short circuiting contacts for movement to open and close said short circuiting contacts, means interconnecting said first and second mechanism means for providing simultaneous movement thereof, said second operating mechanism means including a stationary member, an arm pivotally mounted on said stationary member and carrying one of said short circuiting contacts, a spring to normally bias said pivotal arm to close said short circuiting contacts, a lever interconnected at one end to said interconnecting means, means to adjust the effective length of said lever, and a lost motion coupling means between the other end of said lever and said pivotal arm.
 2. An electric switch assembly according to claim 1 further comprising means for adjusting the position of the stationary contact of said pair of short circuiting contacts in the direction of said movable contact.
 3. An electric switch assembly according to claim 1 wherein said means for adjusting the effective length of said lever comprises an adjustable coupling interposed between said interconnecting means and said one end of said lever.
 4. An electric switch assembly according to claim 1 wherein said lost motion coupling means comprises means defining an elongated slot in said other end of said lever, a first roller having a shaft slidably received in said slot, said stationary member including elongated groove means to slidably receive said shaft of said roller, a second roller mounted on said pivotal arm to cooperate with said first roller to thereby maintain said short circuiting contacts in their closed state, upon closing of said main contacts, until after said main contacts are closed, and to maintain said main contacts in their closed state, upon closing of said short circuiting contacts, until after said short circuiting contacts are closed. 